Need to hide content of program from Android "Overview Screen"

Question

I'm working on an Android app for a security-conscious employer. He's concerned about the screen snapshot that appears on the Overview Screen (a.k.a. the recent-tasks list) leaking sensitive information, and wants me to put up the program's splash screen before the system takes that picture. Unfortunately I haven't found any way to do so.

Things I've tried:

• Inflate the splash screen's View in the onPause function. (No effect, even with bringToFront and setVisibility(View.VISIBLE).)
• Inflate the splash screen's View in onCreate and use bringToFront in onPause. (Again, no effect.)
• Calling setVisible(false) in onPause. (Seemed to almost work, in that the screen blinks to black for an instant when switching away from the program, but it's apparently made visible by the system again before the snapshot.)
• Calling setVisibility(View.INVISIBLE) on the topmost item of the View in onPause. (Seems like it will work, but the snapshot is apparently taken before it takes effect.)

I'm a moderately accomplished Android developer, but I can't help but feel that there's a simple solution that I'm missing.

Answer 1

Personally, I would go with FLAG_SECURE, and simply block display of this stuff everywhere:

public class FlagSecureTestActivity extends Activity {
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    getWindow().setFlags(LayoutParams.FLAG_SECURE,
                         LayoutParams.FLAG_SECURE);

    setContentView(R.layout.main);
  }
}

However, IIRC, you can override onCreateThumbnail() to supply your own image to use for the recent-tasks list. Note that this might have changed with Android 5.0, as they have overhauled that recent-tasks list, so be sure to test your code on a 5.0 device or emulator.

Answer 2

Here is a solution for hiding content of an app by covering it with a splash screen when the app is put into the background. This is not using the FLAG_SECURE technique, I simply override the onPause and onResume methods of the screens and modify the view to show one that covers everything in the back.

First I create my splash screen in a separate file as a relative layout called splash_screen_custom, I also give the relative layout in the file an id customSplash. Note the elevation setting, I ran into an issue where buttons have a preset elevation, so by setting this cover screen to have a high elevation it will cover any buttons(of course you don't need this if you are not covering buttons).

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
     android:id="@+id/customSplash"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="@color/backgroundColor"
     android:elevation="5dp"
         >

     <ImageView
         android:id="@+id/imageView"
         android:layout_width="202dp"
         android:layout_height="157dp"
         android:layout_centerInParent="true"
         app:srcCompat="@drawable/yourImage" />
</RelativeLayout>

In this example my screen I am trying to cover is a relative layout so I am able to simply add and delete my splash screen to it via the addView and removeView methods of view I am trying to cover.

override fun onPause() {

    var parentView = findViewById<RelativeLayout>(R.id.parentView)
    var splashScreen = layoutInflater.inflate(R.layout.splash_screen_custom, null)
    parentView.addView(splashScreen, parentView.width, parentView.height)

    super.onPause()

}

override fun onResume() {
    var parentView = findViewById<RelativeLayout>(R.id.parentView)
    parentView.removeView(findViewById<RelativeLayout>(R.id.customSplash))
    super.onResume()

}

Answer 3

Based on @D.Maul 's answer but the Java version, instead of adding a view, I have tried this. It works fairly but sometimes the recent snapshot shows the app content not sure what to do about it.

private Dialog dialog = null;

@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  dialog = new Dialog(this, android.R.style.Theme_Light);
  dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
  dialog.setContentView(R.layout.customlaunch);
}

@Override
protected void onPause() {
    dialog.show();
    super.onPause();
}
    
@Override
protected void onResume() {
     dialog.hide();
     super.onResume();
}

Answer 4

I just want to provide another version for react-native android based on @D.Maul 's answer:

Bug on some edge cases:

• [1] Dialog is showing
• [2] A very quick SplashScreen is shown when open Camera

Code

@Override
protected void onPause() {
  try {
    // Hide app preview with SplahScreen
    FrameLayout parentView = findViewById(android.R.id.content);
    if (parentView != null && parentView.findViewById(R.id.splash_activity) == null) {
      View splashScene = this.getLayoutInflater().inflate(R.layout.splash_activity, null);
      parentView.addView(splashScene, parentView.getWidth(), parentView.getHeight());
    }
  } catch (Exception e) {
    // do nothing
  }

  super.onPause();
}

@Override
protected void onResume() {
  try {
    // Remove SplashScreen
    FrameLayout parentView = findViewById(android.R.id.content);
    if (parentView != null) {
      parentView.removeView(this.findViewById(R.id.splash_activity));
    }
  } catch (Exception e) {
    // do nothing
  }

  super.onResume();
}

Answer 5

Instead of launching an activity, you might consider launching an app task using ActivityManager.addAppTask(Activity, Intent, ActivityManager.TaskDescription, Bitmap), with which the bitmap you passed in is used as the thumbnail in the overview/recent screen.

Document on this api is here, however, it's only available in Lollipop.